This study investigated postoperative speech function in tongue cancer patients following reconstruction with fasciocutaneous/myocutaneous flaps, to clarify the factor(s) influencing outcome. Eighty-one patients, enrolled from 11 Japanese institutions, were classified into three groups by the site of resection: lateral (N=51), anterior (N=17) and combined (N=13). The lateral group was divided into three subgroups and the anterior group into two subgroups by the size of resection. Mandibulectomy had been performed in 43 patients and radiation therapy in 24 patients. Reconstruction was accomplished by radial forearm flap (N=50), rectus abdominis myocutaneous flap (N=18), pectoralis major myocutaneous flap (N=11), latissimus dorsi myocutaneous flap (N=1) or scapula flap (N=1). Speech function was evaluated with two objective tests and three self-reporting questionnaires. The influence of tongue mobility, age at operation and examination, time interval to examination, and type of flap reconstruction on the functional results was also investigated. Better results were obtained with lateral type resections, smaller excisions, greater tongue mobility, younger patients and longer interval to examination. Mandibulectomy and radiation therapy were negative factors. Type of flap reconstruction had no effect on functional outcome. A treatment method with less functional interference should be developed, particularly for patients anticipated to be in poor functional state postoperatively.